Fluids flowing through a pipeline are typically under pressure to provide motive energy to the fluid. A fluid, namely liquid or gas, which is under pressure from natural sources, such as oil or natural gas from an underground reservoir or well, may be harnessed in whole or part to perform other functions or tasks. At wellsites in the oil and gas industry, for instance, energy is often needed to operate pumps for a variety of purposes, including glycol dehydration, methanol injection, heat tracing of liquid lines, chemical injection, instrumentation, and the like.
At remote wellsites where delivery of electricity is not feasible from an existing power grid, the associated pumps must be operated by other means. Typically, at natural gas wellsites, a portion of the gas from the well's main gas stream is diverted for running the pumps. A significant drawback of these existing arrangements is that the gas is vented to atmosphere as exhaust after being used in the pumps. There appears to be no practical and economical means of recovering such vented gas, particularly since the exhaust is at a significantly lower pressure than that of the gas pipeline. Hence, wellsites operators are faced with the undesireable result of having raw gas emissions to atmosphere, which is believed to be detrimental to the environment, as well as losing the opportunity to sell the vented gas.
What is desired therefore is a novel system and apparatus which overcomes the limitations and problems of prior art pump arrangements. Preferably it should provide a fairly simple and compact device with few moving parts for efficiently and automatically harnessing energy from a pressurized fluid stream in a pipeline to perform a desired task. The system should be fully self contained in that any fluid diverted from the main fluid stream is returned to that fluid stream without any venting to atmosphere. The harnessed energy may be transferred elsewhere mechanically, such as by a movable piston rod, to perform work such as pumping or compressing other fluids, or by other suitable means such as electrical transfer.